how many bytes in an int

[Grant Edwards]

On 2004-08-09, Robin Becker <robin at SPAMREMOVEjessikat.fsnet.co.uk> wrote:
> Grant Edwards wrote:
>> On 2004-08-09, Grant Edwards <grante at visi.com> wrote:
>> 
>> 
>>>The struct module is the only thing I know about.  If you're
>>>worried about the "C" types in the struct module changing
>>>underneat you, you could do a pure Python implimentation of
>>>"python-int" to/from DWORD. It's utterly trivial and shouldn't
>>>take more than one or two lines of code.
>> 
>> 
>> def toLittleEndianDWORD(i):
>>     return ''.join(map(chr,[x&0xff for x in [i,i>>8,i>>16,i>>24]]))
>> 
>> def fromLittleEndianDWORD(s):
>>     return ord(s[0]) + (ord(s[1])<<8) + (ord(s[2])<<16) + (ord(s[3])<<24)
>> 
>
> this simple code will give warnings in 2.3,


> I think struct is really needed.

Like the man said, "struct" doesn't convert to-from integers of
specified byte lengths.  All it has are the C types "int"
"long" "long long", etc.  There is no portable way using struct
to request a 4-byte integer.

> >>> toLittleEndianDWORD(-1)
> '\xff\xff\xff\xff'
> >>> fromLittleEndianDWORD(toLittleEndianDWORD(-1))
> __main__:2: FutureWarning: x<<y losing bits or changing sign will return 
> a long in Python 2.4 and up
> -1

Hopefully that can be fixed?  Python integer objects seem to
get more difficult to work with every year. ;) A few weeks
back, somebody posted code for fixed length Python integer
objects.

-- 
Grant Edwards                   grante             Yow!  YOU PICKED KARL
                                  at               MALDEN'S NOSE!!
                               visi.com